High temperature shaft and method of making the same



Oct. 13, 1936. P. s. MENOUGH HIGH TEMPERATURE SHAFT AND METHOD OF MAKING THE SAME Filed Dec. 19, 1953 INVENTOR Patented Oct. 13, 1936 UNITED STATES PATENT OFFICE HIGH TEMPERATURE SHAFT AND METHOD F THE SAME This invention relates to shafts for use under high temperatures, as, for example, shafts used in continuous normalizing furnaces, and to the method of making such shafts.

The shafts employed in continuous furnaces for transporting the work therethrough were originally water cooled but various objections to this type of shaft have brought the non-cooled shaft into favor. Such shaft is generally made of alloy steel capable of withstanding the intense furnace temperatures and having a hollow body of large diameter so as to make the shaft rigid. The alloys employed are chrome iron alloys either with or without nickel, and it has heretofore been considered impossible to make them except by casting. As stated, such shafts have large diameter hollow body portions, but good design requires that the end portions be of smaller diameter, and the end portions of the body portion are usually connected by hollow tapered portions. The end portions are machined to size to cooperate with bearings, and inorder to make the bearings as small as possible, the journal diameter must be kept small. The shaft extends through a hole in the furnace wall and as this hole must be sealed against the escape of hot gases or the infiltration of cold air, it is desirable to make it as small as possible. Usually where the shaft exits through the furnace wall, the shaft is approximately the same size as the journal.

Furnace shafts of this character have always heretofore been cast in stationary sand molds, a core being employed. The shafts may be I! feet 'or more in lengthand the casting problem is quite diflicult. The core must be supported, usually by chaplets, but even with the utmost precautions, the core frequently sags or floats so that it is eccentric to the mold cavity and the wall thickness of the cast shaft therefore varies. The alloys employed are characteristically sluggish and difiicult to cast, and shrinkage and segregation often takes place at the top of the mold cavity even when risers are employed. Cold shuts are not uncommon. All of these difliculties tend to cause defects which, if apparent when the casting is removed from the sand, may cause rejection of the shaft, or which, if concealed, may cause abrupt failure in service or may greatly shorten the life of the shaft.

1 have found that by employing alloys of proper composition and by following a certain procedure in manufacture it is possible to overcome these several defects and produce a shaft which is uniform as to metallurgical quality and as to circumferential thickness, which is inherently free lurgical composition and of wall thickness.

from defects of casting, and which may be manufactured at relatively low cost. I employ a ferrous alloy comprising 15 to 40% chromium the" balance being principally iron. Other alloying metals may be used, as, for example, nickel, but 5 where nickel is employed I prefer that the sum of the nickel and the chromium shall not be less than 20% and not more than 60%. Alloys within the range stated may be centrifugally cast to form a blank and the process of centrifugal casting insures uniformity of metal- This uniformity of wall thickness cannot be obtained by casting against a core. It is well understood in the art that if any casting can be so designed that it will cool uniformly in all sections, there will be no shrinkage strains and no warpage. It will, therefore, be readily appreciated that due to the uniformity of wall thickness obtained by centrifugally casting the shaft which I provide, it will cool uniformly and there will be no cooling strains or warpage. The blanks thus formed are necessarily of. substantially uniform inside diameter and, as stated, it is desirable that the finished shafts shall have reduced end portions. I have discovered that blanks of the stated composition, when so formed, may be successfully hot worked in their end portions so as to reduce the diameters of such portions, thus forming the desired shaft. It has been heretofore considered commercially impractical to swedge or otherwise hot work such alloys.

I have found that as the diameter of the end portion is reduced, the wall thickens. It is necessary to cut a key-way in one end of the shaft for the attachment of a driving gear or sprocket wheel, and this additional wall thickness makes this possible without the necessity of having the key-way out completely through the wall of the journal end of the shaft. There is always a tendency for the hearings to run hot in a shaft of this type, and this additional thickness of the journal wall tends to prevent the passage of heat from the hot gases in the bore of the shaft to the bearings which are immediately exterior to the journal wall. This is of considerable importance as the ferrous alloy of the journal wall conducts heat only about one-third as rapidly as ordinary steel.

In the accompanying drawing illustrating present preferred embodiments of my invention;

Figure 1 is a transverse section through a centrifugal mold showing a shaft blank cast therein; Figure 2 is a perspective view of the blank;

sistance to furnace gases.

Figure 3 is a view showing the blank with the end portions reduced; and

Figure 4 is a similar view showing a modified form of shaft.

Figure 1 illustrates a centrifugal mold comprising a metallic shell 2 mounted for rotation on supporting rollers 3. The shell 2 has a refractory lining 4 constituting the mold proper and end walls i'having openings 6 therein for the intro-.

duction-of the metal. The mold is rotated at high speed and the molten metal is introduced through a pouring spout. The cast blank is indicated at 1.

Figure 2 shows the blank I in perspective. It comprises a body of substantially uniform wall thickness and substantially free of segregations or other metallurgical defects. Any impurities tend to move to theinnermost surface ofthe blank. This is rimportant not only from the standpoint of strength but also because of re- In certain furnaces the atmosphere employed is highly prejudical to long shaft life and this becomes particularly noticeable if there are any metallurgical defects -.on the outer surface which is bathed in the imnace atmosphere.

The blank I may, if desired, be cast with longitudinally extending ribs 8 to receive work supporting discs. These ribs not only act as supports and driving means for the supporting discs,

but'they also serve as stiffeners for the shaft and materially reduce the fiber stress of the shaft also, of course, remain straight. This facilitates the mounting of work engaging discs on the ribs with a minimum amount of machining. Ma-

chining on surfaces which are exposed to high temperatures is at all times to be avoided, if

possible. The chrome and chrome nickel steelsare very tough and difiicult to machine. Furthermore, if the machined surface is examined with a microscope, it will be found to be inter-' laced with a networkof fine cracks, due to the pull of the machining tool, and these cracks have a tendency to open up under high temperatures and under certain conditions to grow to destructive sizes.

I have above stated the ranges of the alloy whichI use. I preferably use an alloy comprising 28 to chromium, 8 to 10% nickel and the balance principally iron. Other alloys which may be employed are- (a) 28% chromium, balance principally iron;

nickel none.

(b) 15% chromium,

cipally iron.

Figure 3 shows the blank 1 withthe endportions reduced. I have indicated swedging or contracting dies D which may be employed for hot working the ends of the blank to bring them to the desired size and shape. that the end portions 9 are of smaller diameter than the body with thickened walls and that nickel, balance minthe end portions are connected to the body portion by tapered portions l0. Generally speaking, it will be necessary if a considerable reduction is effected to reheat the blank one or more times and to use several sets of dies in reducing the balance being principally iron,

. and cause it to It will be noted end portions. I prefer to heat the blank to a temperature of about 2200 F. before swedging.

Figure 4 illustrates a modified form of shaft having a body portion i2 centrifugally cast as above described with inserted and separately formed end portions It. The body I2 is cast with the ends cylindrical as indicated by dotted lines in the drawing. These ends are machined out to provide a snug fit for the end portions l3 and a shoulder I4 against which the end portions l3 are fitted. Preferably the end portions and the body will both be heated to suitable temperature and then the ends of the body will be swedged to tapered form soas to embrace the end portions .l3 and pe ently unite the parts.

After the swedging operation the parts are fur-, .ther secured by welding, as indicated at IS.

The tapered .portion of the body of the shaft may be flattened or slightly squared after swedging in order to relieve the weld of the starting or stopping torque.

I have indicated by dotted lines F in Figure 4 the general location of the furnace wall with respect to the several parts of the shaft, and it will be noted therefrom that the body only is exposed to full furnace temperature, the end portions lying outside the zone of maximum heat and the weld line i5 being likewise remote therefrom.

It will be understoodthat instead of forming a shoulder I4 by machining, the end portions [3 may be otherwise properly located in the body l2, as, for ex ple, by depositing weld metal within the body, wise.

I have illustrat anddescribed a preferred embodiment of the invention and certain modifications thereof. It will be understood, however, that these are by way of example only and that the invention may be otherwise embodied or practiced within the scope of the following claims.

I claim? 1. In the process of making a high temperature shaft, the steps consisting in centrlfugally casting a body from a heat resisting ferrous alloy 'containing not less than 15% chromium, the

balance being principally iron and nickel, and working the'ends of the body so asto reduce the diameter thereof. I

2. In the process of making a high temperature shaft, the steps consisting in centrifugally. casting a body from a heat resisting ferrous loy containing not less than 15% chromium, the inserting an end portion into the body and working the overlapping portion of the body so as to reduce its diameter 3. In the process of making a high temperature shaft, ing'a body from a heat resisting ferrous alloy containing not less than 15% chromium, the balance being principally iron, inserting a separate end portion, and working the overlapping portion of the'body so as toreduce its diameter and cause it to embrace the inserted end portion, the overlapping portion of the body and the inserted end portion both being hot while said working is effected.

' 4. In the process of making a high temperature shaft, the steps consisting in'centrifugally casting a body from a heat resisting ferrous alloy containing not less than 15% chromium, the balance being principally iron, inserting an end portion into the body, hot working the overlapping portion of the body so as to reduce its or by the use of siiids, or other:

the steps consisting in centrifugally castembrace the inserted endpojrtion.v

diameter and cause it to embrace the inserted end portion, and thereafter welding the body portion to the end portions 5. In the process of making a high temperature shaft, the steps consisting in centrifugally casting a body from a heat resisting ferrous alloy and working the ends of the body so as to reduce the diameter thereof.

6. In the process of making a high temperature shaft, the steps consisting in centrifugally casting a body from a heat resisting ferrous alloy, inserting an end portioninto the body and working the overlapping portion of the body so as to reduce its diameter and causing it to embrace the inserted end portion.

7. In the process of making a high temperature shaft, the steps consisting in centrifugally casting a body from a heat resisting ferrous alloy, inserting a separate end portion, and working the overlapping portion of the body so as to reduce its diameter and cause it to embrace the inserted end portion, the overlapping portion of the body and the inserted end portion being both hot while said'working is effected.

8. In the process of making a high temperature shaft, the steps consisting in centrifugally casting a body, inserting an end portion into the body, hot working the overlapping portion of the body so as to reduce its diameter and to cause it to embrace the inserted end portion, and thereafter weldingthe body portion to the end portion.

9. A furnace shaft comprising a tubular body, journals for rotatably supporting the .body, said journals being of smaller diameter than the body and having outwardly flaring inner ends adapted to be inserted in the ends of the body, the ends of the body extending beyond the inner ends of the journals being contracted thereabout, to constitute a rigid supporting roll.

10. The device of ,claim 9 characterized by a shoulder on said journals to prevent movement thereof inwardly of said body.

11. The device of claim 9 characterized by the ends of the body extending outwardly of the planes defined by the inner surfaces of the furnace walls, whereby a weld joining the ends of the body and the journals is protected from furnace temperatures. I

12. In a method of making a furnace shaft, the steps including inserting journal members in the ends of a tubular body and swedging the ends of the body over the inserted ends of the journals whereby embrace them firmly.

13. A furnace shaft comprising a tubular body, journals inserted in the ends of the body, and a weld connecting the body and journals, said body being longer than the inside width of the furnace in which it is to be installed, whereby to locate said weld within the furnace wall and protect it from the'high temperature inside the furnace.

14. A furnace shaft comprising a tubular body, journals engaging the ends of the body, and welds connecting said journals to the ends of said body, the distance between said welds being greater than the inside width of said furnace in which said shaft is to be installed whereby when said shaft is installed, said welds will be located outwardly of the inner sides of said walls and protected thereby against the heat of the furnace.

15. A furnace shaft comprising a tubular centrifugally cast body portion having external ribs integral therewith and extending longitudinally thereof, supporting members telescopically engaging the ends of said body portion, welds for rigidly connecting said members to said body portion, each of said members having a journal portion of a diameter materiallyless than said body portion, said body portion being of such length that said welds will. be located outwardly of the inner surfaces of the walls of the furnace in which said shaft is to be installed whereby said welds will be .protected from the heat of the furnace.

16. A furnace shaft comprising a centrifugally cast body, essentially tubular, journals inserted in the ends of the body, and a weld connecting 5 portion forming a journal for said shaft, said tapered portion telescoping within an end of said body and seated against said shoulder, the ends of said body portion being swedged onto said tapered portions for rigidly hoiding'ithe same'against said'shoulders.

PAUL S. MENOUGH. 

